1. Field of the Invention
The present invention relates generally to cable connectors for differential transmission, and more particularly to a cable connector for differential transmission employed to transmit a high-speed signal.
2. Description of the Related Art
There are two types of data transmission methods: a normal transmission method and a differential transmission method. The normal transmission method employs an electric wire for each data item. The differential transmission method, using a pair of electric wires for each data item, simultaneously transmits a “+” signal to be transmitted and a “−” signal equal in magnitude and opposite in direction to the “+” signal. The differential transmission method, which has the advantage of being less susceptible to noise compared with the normal transmission method, has been used more widely. A cable connector for differential transmission (a differential transmission cable connector) has a plug provided to an end of a differential transmission cable and covered by a shield cover. The differential transmission cable connector is applied to the differential transmission method, and is used, for instance, to connect a computer and a server.
FIGS. 1 and 2 are an exploded perspective view and a sectional view, respectively, of a conventional differential transmission cable connector 10. In FIGS. 1 and 2, X1–X2, Y1–Y2, and Z1–Z2 indicate the directions of width, length, and height, respectively, of the differential transmission cable connector 10.
FIG. 3 is a sectional view of a differential transmission cable 20. Referring to FIG. 3, the differential transmission cable 20 includes multiple pair wires 21 inside a tube of a double-covering structure formed of an outer cover 27 and a braided shield 28. Each pair wire 21 includes paired first and second covered signal wires 22-1 and 22-2 for differential signal transmission and a drain wire 25, which are bundled with a metal tape wound spirally therearound. As shown in FIG. 6, the first and second covered signal wires 22-1 and 22-2 and the drain wire 25 extend from an end of the pair wire 21. The ends of the first and second covered signal wires 22-1 and 22-2 are processed so that first and second signal wires 23-1 and 23-2, respectively, are bared and exposed. The first and second signal wires 23-1 and 23-2 form a pair line.
Referring to FIGS. 1 and 2, in the differential transmission cable connector 10, the first and second signal wires 23-1 and 23-2 and the drain wire 25 extending from each of the multiple pair wires 21 extending from the end of the differential transmission cable 20 are connected by soldering to the corresponding Y1-side terminals of a relay board 12, which is fixed to the Y1 side of a contact assembly 11. Shield covers 31 and 32 cover the contact assembly 11, the relay board 12, and the end portion of the differential transmission cable 20. In the differential transmission cable connector 10, the contact assembly 11, the relay board 12, and the end portion of the differential transmission cable 20 form a data transmission channel.
Japanese Laid-Open Patent Application No. 2003-059593 discloses a conventional cable connector for differential transmission.
Focusing on the shield between adjacent data transmission channels, the differential transmission cable connector 10 has a problem in the part of the relay board 12. On both the upper and lower surfaces of the relay board 12, wiring patterns extending along the Y-axis are formed side by side along the X-axis. The vertically aligned upper and lower wiring patterns form a wiring pattern pair so that the wiring pattern pairs are formed side by side along the X-axis on the relay board 12. Accordingly, for structural reasons, it is difficult to provide as good a shield between each two adjacent wiring pattern pairs as in the contact assembly 11.
In these years, signals processed by computers and servers have become higher in speed, so that adverse effects on transmission characteristics due to low shielding provided by the relay board 12 have become unignorable.
Further, in terms of production costs, it is required that differential transmission cable connectors be structured so that they can be assembled with efficiency with good productivity.